When an object moves with respect to stationary references such as a ground plane, fixed points, lines or reference surfaces, knowledge of the object's inclination with respect to these references can be used to derive a variety of its parameters of motion as well as its pose. Over time, many useful coordinate systems and methods have been developed to track the pose of objects and to parameterize their equations of motion. For a theoretical background the reader is referred to textbooks on classical mechanics such as Goldstein et al., Classical Mechanics, 3rd Edition, Addison Wesley 2002.
In one specific field it is important to know the pose of an object to derive the position of its tip while it contacts a plane surface. Various types of elongate objects can benefit from knowledge of their pose and position of their tip, and more precisely the absolute position (in world coordinates) of their tip while it is in contact with a plane surface. These objects include walking canes when in touch with the ground, pointers when in touch with a display or projection surface, writing devices when in touch with a writing surface, and styluses when in touch with an input screen.
The need to determine the absolute position of the tip or nib is deeply felt in the field of input devices such as pens and styluses. Here, the absolute position of the tip has to be known in order to analyze the information written or traced by the user on the writing surface. Numerous teachings of pens and related input devices providing relative tip position and absolute tip position are discussed in the prior art. Some of these teachings rely on inertial navigation devices including gyroscopes and accelerometers as described in U.S. Pat. Nos. 6,492,981; 6,212,296; 6,181,329; 5,981,884; 5,902,968. Other techniques combine inertial navigation with force sensing as described in U.S. Pat. Nos. 6,081,261; 5,434,371. The prior art also teaches capturing and analyzing forces applied to the pen point in U.S. Pat. No. 5,548,092. Still other techniques rely on triangulation using signal receivers and auxiliary devices on or adjacent to the writing surface as found in U.S. Pat. Nos. 6,177,927; 6,124,847; 6,104,387; 6,100,877; 5,977,958; 5,484,966. It should be noted that various forms of radiation including short radio-frequency (RF) pulses, infra-red (1R) pulses, and ultrasound pulses have been taught for triangulation and related techniques. A few examples of yet another set of solutions employing digitizers or tablets are discussed in U.S. Pat. Nos. 6,050,490; 5,750,939; 4,471,162.
The prior art also addresses the use of optical systems to provide relative, and in some cases, absolute position of the tip of a pen or stylus on a surface. For example, U.S. Pat. No. 6,153,836 teaches emitting two light beams from the stylus to two receivers that determine angles with respect to a two-dimensional coordinate system defined within the surface. The tip position of the stylus is found with the aid of these angles and knowledge of the location of the receivers. U.S. Pat. No. 6,044,165 teaches integration of force sensing at the tip of the pen with an optical imaging system having a camera positioned in the world coordinates and looking at the pen and paper. Still other teachings use optical systems observing the tip of the pen and its vicinity. These teachings include, among others, U.S. Pat. Nos. 6,031,936; 5,960,124; 5,850,058. According to another approach, the disclosure in U.S. Pat. No. 5,103,486 proposes using an optical ballpoint in the pen. More recently, optical systems using a light source directing light at paper have been taught, e.g., as described in U.S. Pat. Nos. 6,650,320; 6,592,039 as well as WO 00217222 and U.S. Pat. Appl. Nos. 2003-0106985; 2002-0048404.
In some prior art approaches the writing surface is provided with special markings that the optical system can recognize. Some early examples of pens using special markings on the writing surface include U.S. Pat. Nos. 5,661,506; 5,652,412. More recently, such approach has been taught in U.S. Pat. Appl. 2003-0107558 and related literature. For still further references, the reader is referred to U.S. Pat. Nos. 7,203,384 and 7,088,440 and the references cited therein.
Most of the prior art approaches listed above are limited in that they yield relative position of the tip on the writing surface. Tablets and digitizers obtain absolute position but they are bulky and inconvenient. Of the approaches that provide absolute position of the tip without tablets by using optical systems, most rely on observing the relationship of markings provided on the writing surface to the tip of the pen. This approach is limiting it that it requires a specially-marked writing surface, which acts as a quasi-tablet.
In addition to being cumbersome, state-of-the-art pens and styluses employing optical systems usually generate a limited data set. In fact, most only provide data corresponding to the trace traversed on the writing surface. Meanwhile, there are many applications that could benefit from a rich stream of data from the pen or stylus. In fact, the prior art indicates many situations in which interactions between a user employing a pen or stylus and a machine, e.g., a computer, are limited. For a few examples of applications and systems that could benefit from a richer stream of data from the pen or stylus the reader is referred to U.S. Pat. Nos. 6,565,611; 6,502,114; 6,493,736; 6,474,888; 6,454,482; 6,415,256; 6,396,481 and U.S. Pat. Appl. Nos. 2003-0195820; 2003-0163525; 2003-0107558; 2003-0038790; 2003-0029919; 2003-0025713; 2003-0006975; 2002-0148655; 2002-0145587 and U.S. Pat. No. 6,661,920.